We previously described the induction by salicylates and other weak acids of nonheritable antibiotic-resistance in Escherichia coli and other bacteria. Two mechanisms appear to underlie these effects. First, uptake of cephalosporins through the outer membrane into the periplasmic space is reduced 4-5 fold in E. coli treated with salicylate. Thus, salicylate affects the permeability of the outer membrane. Second, since some Gram positive bacteria (without an outer membrane) also show increased antibiotic-resistance in the presence of salicylate, another mechanism must be involved, possibly one that affects inner membrane function. Additional effects of salicylate on E. coli have been demonstrated: decreased uptake of beta-galactosides; altered susceptibility to kanamycin; interference with isoleucine-valine metabolism.